1. Field of the Invention
The present invention relates to the field of collators and specifically to devices for collating sheets of paper. More particularly, the invention relates to a collator having an improved mechanism for removing electrical charges from the sheets as they are collated.
2. Description of the Prior Art
It is generally known that when sheets of paper are handled, such as when making copies in an electrophotographic copying machine, the sheets often become electrically charged. Such an electrical charge may make transportation of the sheets in the copier more difficult. Also, when the sheets are collated in a pile, the electrical charge accumulated in the pile may be large enough that a person touching the pile receives an electric shock. This undesirable phenomenon can be obviated if the surface on which the sheets are collated is made from an electrically insulating material and a means is used to discharge the deposited sheets as much as possible.
A typical collating device is disclosed in U.S. Pat. No. 3,957,264. This device has an electrically insulating receiving surface which is curved in one direction and which has upright edges. It also has a brush extending transversely from the direction of sheet transport, with conductive bristles above the receiving surface for removing electrical charges. The electric field between a charged sheet on the receiving surface and the sharp ends of the bristles is supposed to ionize the air above the sheet, creating an atmosphere in which the sheet charge is reduced.
A major disadvantage of the device described in U.S. Pat. No. 3,957,264, however, is that the brush electrode is situated relatively far away from the receiving surface and the charged sheets lying thereon, so that it will have very little effect on reducing sheet charge when only a few sheets are collated. In such a case, therefore, strong residual charges will remain on the few collated sheets.
Japanese Patent Abstract 57-27272 of Fuji Xerox KK relates to a discharge tray. The disclosure, however, teaches that a substantial portion of the discharge tray is made of conductive material instead of insulating material. Even with this substantial area of conductive material, there is no way to assure that any sheet other than the first sheet will be discharged. Thus, this device will have very little effect on reducing sheet charge, unless the other sheets, by chance, happen to come into contact with the conductive material.
Japanese Patent Abstract 56-116048 of Cannon KK relates to a storage tray for paper, not to a collator. The discharge problems associated with feeding a prestacked pile of paper and those associated with collating individual sheets are different. For example, the metal retaining members of a storage tray may directly abut and contact the prestacked papers. This is not possible in a collator because the copying machine cannot expel copies with enough precision to permit the effective discharge of the sheets through rubbing with metal sides. Thus, there exists a need for an improved method of discharging residual charge in a collator which assures that each sheet will be discharged.